Field of the Invention
This invention relates to a dental implants used to form root analogues for the attachment of dental prostheses, and more particularly, to such a dental implant having no externally threaded surfaces, particularly configured for use in areas of relatively low bone density.
2. Background Information
Cylindrical dental implants have been in use since 1976, with several different designs being incorporated into dental therapy. A dental implant is used where there are missing teeth, to act as a root analogue supporting a dental prosthetic device fitting on top of the implant. Such an implant typically has an internal threaded hole, extending inward from a hexagonally shaped surface portion, to be used for the attachment of a dental prosthetic device. The prosthesis is then screwed onto the implant, with an intermediate portion of the prosthesis engaging the hexagonal portion of the implant to prevent rotation. The implant includes a generally cylindrical portion extending from the surface portion to an apical portion at the opposite end.
Some dental implants have helically threaded exterior cylindrical surfaces and are normally inserted in dense bone areas such as the front jaw. These implants are literally screwed into properly sized holes drilled into the bone. Other dental implants are generally cylindrical shaped, without threads, and are placed into holes previously drilled into the bone. These non-threaded implants have surface designs adapted for the attachment to new bone growth. Conventional non-threaded cylindrical implants have openings extending through their apical portions for the intended purpose of permitting a space to accommodate new bone growth. However, recent research has shown that new bone growth does not predictably fill these openings. For example, the article by M. S. Block, I. M. Finger, M. G. Fontenot, and J. N. Kent, entitled "Loaded Hydroxylapatite and Grit-Blasted Titanium Implants in Dogs", in The International Journal of Oral & Maxillofacial Implants, Volume 4, pages 219 through 25, clearly shows that new bone does not completely fill these openings.
Chemical coatings and textured surfaces are also used to promote the attachment of bone to the implant. The Block et al article evaluated the response of canine mandibular bone to loaded hydroxylapatite coated and grit blasted titanium dental implants, and concluded that while soft tissue pocket depths were not statistically different, and crestal bone loss was not significantly different, the hydroxylapatite coated implants had a statistically significant greater amount of bone contacting their axial and apical surfaces. The implants used in this study included cylindrical axial portions with apical portions having cross drilled radial holes extending therethrough, and hemispherical apical ends.
One important function of the dental implant is the transmission of forces, generated by chewing actions on the prosthesis, into forces applied to the bone surrounding the implant, at stress levels compatible with the growth and maintenance of health bone tissue. Such stresses stimulate the surrounding bone, and, in accordance to Wolff's Law, if bone is not stimulated it will atrophy, whereas, if bone is over stimulated it will resorb in a process in which the calcified matrix dissolves away, lowering the density of the bone.